1. Field of the Invention
The present invention relates to a tool having a wear-resistant and adhesion-resistant amorphous carbon film formed at the surface of rotating tools (drills, end mills, reamers, and the like), an indexable insert used for milling cutters and turning tools, and cutting-off tools (cutters, knives, slitters and the like). The present invention also relates to a method of fabricating such a tool.
2. Description of the Background Art
The conventional requirements with respect to cutting tools include the capability of increasing the lifetime of the tool by minimizing any damage at its surface and carrying out machining at high efficiency as well as finishing the workplace with high quality (maintaining the surface configuration, the hardness of the parent material, the dimension accuracy and the like).
Recently, there is a strong demand for the development of a tool that reduces the cutting resistance and a tool without degradation in the lifetime and cutting efficiency even if the amount of oil agents for cutting is reduced from the standpoint of protecting the environment and saving energy.
The material of the workpiece now includes a variety of types. In the case where the workpiece includes soft metal such as aluminum alloy, a non-ferrous metal such as titanium, magnesium, or copper, an organic material, or a material including hard particles such as graphite, or in the case of working on a printed circuit board or bimetallic cutting of an iron type material and aluminum, problems are noted such as residuals adhering to the cutting edge of the cutting tool to increase the cutting resistance, and, in some cases, cause chipping at the cutting edge. The wear of the tool used on such specific workpieces has become more significant.
The demand for reducing the cost drastically without degrading the performance is strong in the field of metal machining.
In the specific field of working on aluminum, aluminum alloy, or organic material, the diamond tool has been traditionally used. As to such tools having a diamond film formed on the base, the growing rate of the diamond film differs greatly depending upon the crystal orientation. The surface asperity is so great that the complex shape of the tool must be polished if the tool is to be used for high-precision processing.
Since diamond is the hardest available material, grinding of a diamond film requires the usage of diamond that is extremely expensive. This attributes to the increase in cost.
Furthermore, since a crystal growth speed varies in the crystal direction drastically, to get a smooth grinding surface, a film of 20-30 μm in thickness must be prepared in the case of a diamond film, as compared to the general thickness of 2-3 μm for a ceramics coated film such as TiN, obtained by PVD (Physical Vapor Deposition) coating. Formation of a diamond film is carried out while graphite that is deposited at the same time is removed by etching. Therefore, the film growth rate becomes as slow as less than {fraction (1/10)} the rate of normal PVD coating. There was a problem that the fabrication cost including the coating process is extremely high.
As to tools made by brazing a diamond sintered compact on a base, it is difficult to fabricate the tools of complicated shape or the tools as fine as several millimeters in diameter.
Japanese Patent Laying-Open No. 2000-176705 discloses a tool member having a hard material including TiN, TiCN, TiAlN, Al2O3 or a combination thereof coated, and then further coated with a hard carbon type lubricating film. In order to form an economic hard carbon type lubricated film that has stable durability and suitable for mass production, the inventors in this publication propose formation of an intermediate layer of a component including silicon and carbon or silicon, carbon and nitrogen, followed by a formation of a silicon layer of at least 0.02 μm and not more than 0.5 μm in thickness under and in contact with the bottom of the intermediate layer.
The hard carbon coated film at the outermost surface layer disclosed in this publication inevitably includes hydrogen atoms in the film since formation is conducted through ion plating and plasma CVD (Chemical Vapor Deposition) using hydrocarbon type gas. It is generally known that hydrogen atoms in hard carbon film are desorbed from the film at the temperature of at least approximately 350° C. in the atmosphere. Following desorption of hydrogen, the hard carbon coated film is modified into graphite. The hardness is significantly degraded. Such a coated film is not suitable for usage in a severe cutting environment.